a) Field of the Invention
The present invention relates to an optical head assembly used for recording to and reproducing from an optical recording medium.
b) Description of the Related Art
An optical head assembly for reproducing optical recording media such as CDS (compact disks), DVDs (digital video disks), etc. is constructed such that a laser light from a laser light source is converged on a recording surface of an optical recording medium through a primary objective lens, a returning light from the recording medium is detected by an optical detector, and data recorded on the optical recording medium is reproduced based on the detection results. Japanese Patent Application Tokkai H6-302011, for example, has disclosed an optical head assembly having two diffraction grating means placed in an optical path between the laser light source and objective lens, one of which splits a laser light from the laser light source into multiple laser beams and the other of which separates a returning from the laser light of an optical recording medium and from the laser light source and guides the returning light to an optical detector. In addition, Japanese Patent Application, Tokkai H6-76340 has disclosed an optical head assembly in which a laser light source, optical detector, and two diffraction grating means are made as an entity.
The diffraction grating means has a predetermined diffraction pattern to obtain a desired diffraction property. Therefore, if the diffraction grating means is not at a right angle with respect to the optical axis of the optical head assembly or the optical axis of the assembly and the diffraction pattern are not in a predetermined positional relationship, a problem occurs in that the returning light from the optical recording medium will not be efficiently guided to the optical detector. Conventionally, the diffraction grating means is constructed such that a mounting position and angle can be changed arbitrarily. The mounting position and angle of the diffraction grating means are adjusted while the diffracting direction of the diffraction grating is identified using a microscope or the output of the optical detector is observed.
While the mounting position and facing direction of the diffraction grating means can be changed arbitrarily, however, it takes time to adjust them to an optimal condition. In other words, as the optical head assembly disclosed in Japanese Patent Application H6-302011 in which two diffraction grating means are used, the mounting position and the like needs to be adjusted for each diffraction grating. Therefore, it is difficult to finish adjustment in a short time, increasing cost necessary for the operation. In addition, Japanese Patent Application H6-76340 disclosed that the laser light source, optical detector, and two diffraction grating means are made as an entity. With this configuration, while there is an advantage of making the optical system compact and facilitating the assembly of the optical system, a problem remains that it takes time to adjust the mounting position of the diffraction grating means with respect to the laser light source and the like when making the system as an entity.